Device for producing semi-product tubes of constant inner diameter with thinned ends

ABSTRACT

In a two-high mill for the longitudinal rolling of tubes on a short arbor with round roll passes, in which one of the rolls is installed for possible displacement to vary the clearance therebetween. The roll is displaced by a variable drive, in the direction of increasing the clearance in rolling the front end of the tube and in that of decreasing the clearance in rolling the rear end thereof. The same drive holds the roll in maximum and minimum clearance positions. The variable drive is operated through a directional and speed control system thereof.

United States Patent [191 Gulyaev et al.

[ 1 Feb. 11,1975

[ DEVICE FOR PRODUCING SEMI-PRODUCT TUBES OF CONSTANT INNER DIAMETER WITH THINNED ENDS [76] Inventors: Gennady Ivanovich Gulyaev, ulitsa Sevastopolskaya, l0, kv. 52, Dnepropetrovsk; Jury Nikolaevich Neznamov, ulitsa Chubarya. l3, kv. 62, Nikopol; Anatoly lonovich Nechiporenko, ulitsa Vysokovoltnaya, 28/39; Viktor Yakovlevich Ostrenko, ulitsa Komsomolskaya, 65, kv. 44, both of Dnepropetrovsk; Petr Ivanovich Kutsenko, ulitsa Pestelya 4, Nikopol; Viktor Kharitonovich Kurilenko, ulitsa Korbuta, 7, kv. 3, Nikopol; Ivan Vasilievich Ermolov, ulitsa lenina, 56, kv. 8, Nikopol; Alexandr Ilich Chekmarev, ulitsa Karla Marxa, 108, Nikopol; Vladimir Grigorievich Voronko, ulitsa Lenina, 63, kv. 4, Nikopol; Ivan Petrovich Boiko, ulitsa Rostovskaya, 22, kv. 30, Nikopol; Vladimir Romanovich Mamontov, prospekt Kirova, 76, kv. 45; Jury Ivanovich Pustovoichenko, ulitsa Sofii Kovalevskoi, 55, kv. 46, both of Dnepropetrovsk; Gennady Mikhailovich Volovik, ulitsa 40 let Oktyabrya, 1, kv. ll, Nikopol; Vladislav Georgievich Zakharenko, prospekt Lenina, l2, kv. 7, Nikopol; Viktor Prokhorovich Paschenko, ulitsa imeni Pravdy, 7, kv. 75,

O O uuuuuu an E i Q Nikopol, all of U.S.S.R.

[22] Filed: Dec. 19, 1973 [21] Appl. No.: 426,220

Primary ExaminerMilton S. Mehr [57] ABSTRACT In a two-high mill for the longitudinal rolling of tubes on a short arbor with round roll passes, in which one of the rolls is installed for possible displacement to vary the clearance therebetween. The roll is displaced by a variable drive, in the direction of increasing the clearance in rolling the front end of the tube and in that of decreasing the clearance in rolling the rear end thereof. The same drive holds the roll in maximum and minimum clearance positions. The variable drive is operated through a directional and speed control system thereof.

12 Claims, 16 Drawing Figures PATENTEDFEBI 1191.5

sum 0103 10 Nome PATENTED 3.864.951

- sum UZUF 10 PATENTED v 3.864.951 'SHEET cam 10 PATENTEDFEBI 1 ms SHEET csur 1o PATENTEUFEBHIHTS sum user 10 PATENIEDFEBI 1 ms SHEET 0s or 10 SHEET USOF 1O PATENTEBFEBI 1 I975 I I I I l I DEVICE FOR PRODUCINGSEMI-PRODUCT TUBES OF CONSTANT INNER DIAMETER WITH T HINNED ENDS BACKGROUND OF THE INVENTION The present invention relates to improvements in tube rolling installations and more particularly to devices for producing semiproduct tubes of a constant inner diameter with thinned ends, especially tapered ones, intended for further stretch-reduction.

PRIOR ART Application is known of tube rolling installations with stretch reducing mills for producing a wide range of high-quality rolled tubes. However due to the transistory character of tensioning in reducing end portions of a tube, its wall becomes thicker over a considerable length of the end portions thereof as against the wall thickness in the middle portion of a tube and extends beyond the allowable tolerances. Thick-wall ends of tubes are cut off for scrap. The excess metal consumption reduces the efficiency of tube rolling installations.

Several methods are known at the present time to shorten the length of tube thick ends. The first method is that tubes before reduction are butt-welded into a continuous tube. Attempts for realizing this method were of no success because the tubes, when handled in a stretch-reducing mill, broke up across the welded joints as stresses in the metal caused by the tension account to 70-80 percent of the metal ultimate strength at the given temperature.

The second method implies the shortening ofthe stand spacing in the stretch-reducing mill because research has shown that the length of the tube thick end portions is determined to a considerable degree by this very parameter of the mill. This method entails a substantially complicated stretch-reducing mill design permitting no complete elimination of the thick tube end portions because of the stand spacing being a nonvanishing value.

The third method is that by varying the rotational speed of the rolls of the stretch-reducing mill in rolling the tube end portions, such rolling conditions are established which lead to shortening the length of the tube thick ends. However, this method is not capable of complete elimination of the tube wall end thickening.

A method has been developed by which the tubes are reduced with the end portions thereof thinner as against that of the tube middle portion. The capacity of the wall thinning-out is chosen keeping in mind that as a result of unavoidable thickening of the tube wall end during the process of reduction, the wall thickness becomes equal to that of the tube middle portion.

The experiments conducted have shown, in particular, that the tapered character of tube wall thinning-out before the reduction process, makes it possible to fully compensate for the thickening occurred.

Methods of turning the tube end wall by metalcutting machine-tool have been suggested for producing tubes with thinned-out end walls, which, however, entails a large loss of metal to shaving scrap and necessitates a large nunber of metal-cutting machine-tools to be available.

Thinning-out the tube end wall by way of forging has been also proposed. This requires the tube rolling installation equipment to incorporate forging machines and additional means forheatingthetube ends'priorto forging, thus complicating the tube-making process.

A method is known byproducing tubes with a thinned-out wallat the ends .thereof by rolling mills with a varied roll profile, on a long arbor. Thesemills are installed upstream of the stretch-.reducing'mill and the tube end wall is rolled-off on a long'arbor. The principal disadvantage of this'method for producing tubes with thinned-out ends is that the extraction of thelong arbor from the tube resultstin the collapsing of thetube endand unavoidable cutting off the ends over a considerable portionof the tube. Moreover, the installation'of such mills requires an extended production floor area and extra processv operations.

OBJECTS AND SUMMARY OF THE INVENTION An object of the present invention is to reducemetal consumption in manufacturing tubes from semiproduct tubes with tapered end portions.

Another object of the present invention is to provide special equipment to manufacture semi-product tubes with thinned-out end portions, on the basis of the existing equipment.

One more object of the present invention is to provide equipment for the manufacture of a wide range of semi-product tubes. Among other objects should be noted an improvement in the quality of tubes made from semi-product tubes with tapered ends.

These and other objects are achieved due to the provision of a device for producing semi-product tubes with thinned ends of constant inner diameter intended for further rolling in the stretch-reducing mill, according to the invention, comprising a two-high mill for longitudinal rolling of tubes on a short arbor with round roll passes, with at least one of the rolls having a variable drive for a gradual displacement of said roll during the tube rolling process in the direction of altering the clearance between the rolls to increase the clearance in rolling the front end of the tube and to reduce it in rolling the rear end thereof and also to fix the rolls at a maximum and minimum given clearance therebetween, and a system of directional and speed control for the displacement of the rolls by means of said drive.

An advantage of the present invention is that it allows the existing equipment to be utilized, requires no additional production area and also makes it possible to manufacture a wide range of semi-product tubes of most diversified thinned end shaping.

In the present device, use may be made of a roll displacement drive having two synchronously operating hydraulic cylinders with an adjustable stroke connected to the roll journals and displacing the roll to the extreme positions in which one position corresponds to the minimum clearance between the rolls and the other extreme position corresponds to the maximum clearance between the rolls, with the hydraulic cylinder powering system incorporating controllable throttle valves to vary the rate of the hydraulic fluid flow.

This drive can be installed in the mill bed thus allowing the rolling mill, without extending its dimensions, to be used for the manufacture of semi-producttubes with thinned ends.

A hydraulic cylinder stroke regulator may take the form of a plug entering the cylinder inner space, with shoulders resting on the cylinder through a wedgeshaped gasket installed for apossible displacement and locking in the given position to adjust the cylinder stroke.

Conveniently, the variable drive control system comprises a thinned end portion length control unit connected to the drive and generating signals to control its speed for varying the roll displacing speed, and a tube end position sensor installed behind of the rolls at the tube entering side, sensing the tube front end position and generating a signal for the commencement of a gradual parting of the rolls from the minimum to the maximum given clearance and also sensing the tube rear end position and generating a signal for a gradual bringing together of the rolls until the given minimum clearance is obtained.

Incorporation of the thinned end portion length control unit in the drive control system permits any length of thinned portions to be obtained in the manufacture of a varied tube stock with a high accuracy maintained in the manufacture of the given stock.

It is wise to provide in the control system two roll extreme position sensors and an electric pulse generator with a recurrance frequency proportional to the rolling speed, and to give the tapered end portion length control unit a generator pulse counter to be connected to said generator through a commutator controlled by the extreme position sensors whose signals operate the commutator to connect or disconnect the counter to and from the generator, respectively resulting in the total number of pulses entering the counter to be proportional to the length of the tapered portion. The pulse counter should be represented by one with a variable output, generating an electric signal when the number of pulses entering the counter deviates from a certain given value.

Conveniently, the control system incorporates an electric means to determine error in the tapered portion length relatively to the given value, including two parallel electric circuits with a coincidence circuit on the output of each of them connected to the generator, and two flip-flops, with one of them connected to the pulse counter output and both coincidence circuits and the other to the counter output and one of the coincidence circuits so that depending on the state of the flipflops, one of the coincidence circuits opens while the other remains closed, resulting in an electric signal occurring on the output of coincidence circuits, characterizing the value and sense of an error.

An error determination means permits high accuracy in following the length of the thinned portions as well as the drive operational control when said length deviates from the given value.

To improve operation of the drive in the device, the tube end position sensor is composed of two elements registering the passage of the tube ends, installed in one-after-another succession on the side where the tube enters the rolls in its forward travel, and a drive engaging unit is connected to the sensor elements and adapted to produce an output signal, on receiving a signal from one of the sensors, to be transmitted to the drive to part the rolls and, on receiving a signal from the other sensor, to produce an output signal to bring together the rolls, with the engaging unit being provided with an output signal time delay means to regulate the drive engaging moment relatively to the moment of gripping the tube by the rolls and the moment of the tube coming out of the rolls.

It is feasible that the control system includes a roll displacement start delay control unit connected through its output to a minimum roll clearance sensor and to a roll load sensor, and generating a signal proportional to a time interval between the signals of these latter sensors, with the delay control unit output being connected to the drive engaging unit delay means through a delay setter to regulate the delay value depending on an error at the commencement of the roll displacement.

For rolling tubes having cylindrical thinned ends. the thinned end portion length control unit should be provided with a plurality of identical delay error determination means, each of which is to effect control over the front or rear end in the corresponding pass of the tube in the mill, whereas the commutator should be multichannel to cut in for operation the corresponding pairs of error determination means, with the control system being provided with a sensor of a successive tube pass number, connected to said commutator for the switching thereof.

The hydraulic cylinder powering system includes two parallel-connected controllable throttle valves per each hydraulic line, communicating with both spaces of the cylinders, and pilot valves operate the throttle valves, with the pilot valves being connected to the sensor of the successive tube pass number to control their engagement.

To improve the quality of semi-product tubes produced by means of the present device, it is favorable to install at the outlet end of the longitudinal tube rolling mill, a rolling-off mill, in which at least one of the rolls has a variable drive for its gradual displacement in the course of rolling tube ends in the direction of altering the clearance between the rolls to increase the clearance in rolling the front end of the tube and to reduce it in rolling the rear end thereof and also to fix the rolls at the maximum and minimum given clearance therebetween, and also has a roll drive control system setting such a speed and direction of their displacement at which the shape of the semi-product tube produced on the longitudinal rolling mill is being followed.

In order to make the present invention more readily understood, an actual embodiment of the process of tube manufacture semi-product tubes with thinned end portions will be described with reference to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic layout of the tube rolling installation for producing tubes on which before stretchreduction, the end wall is thinned-out according to the given law;

FIG. 2 is a section taken along the line IIII of FIG.

FIG. 3 is a layout of the hydraulic drive for displacing the rolls of the mill;

FIG. 4 shows the drive hydraulic system of FIG. 2;

FIG. 5 is an electric block diagram of the drive control system;

FIG. 6 is a key electric diagram of the drive engaging unit;

FIG. 7 is a key electric diagram of the delay control unit;

FIGS. 8a and 8b show the shapes of a semi-product tube when the moments of gripping the tube by the rolls and of their parting are in non-coincidence;

FIG. 9 is an electric diagram of the error determination means;

FIG. is a key diagram of the signal delay setter;

FIG. 11 is a key diagram of the thinned portion length control unit;

FIG. 12 is a layout of the rolling-off mill drive hydraulic system;

FIG. 13 is a diagram of the rolling-off mill drive control system;

FIG. 14 is a key diagram of the engaging unit;

FIG. is a diagram of the rolling-off mill drive delay control unit; and

FIG. 16 is a diagram of the thinned portion length control unit in the rolling-off mill.

DETAILED DESCRIPTION OF THE DRAWINGS The installation for manufacturing tubes from semiproduct tubes of constant inner diameter with tapered end portions comprises an annular or holding furnace 1 (FIG. 1) for heating billets before rolling, a roll or disk piercing mill 2 for producing hollow billets, a device for producing semi-product tubes of a constant inner diameter with tapered end portions from hollow billets, comprising a mill 3 for the longitudinal rolling of tubes on a short arbor 4 with the variable system of control (not shown in FIG. 1) of the direction and speed of the drive for displacing rolls 5 and 5 of this mill, with the rolls being installed for a possible altering of the clearance between the top and bottom rolls (FIG. 1 shows the bottom roll only), and also a rollingoff mill 6 installed on the outlet from the mill 3. Apart from that the above, the installation includes a furnace 7 for heating the thinned end portions of the tubes and a stretch-reducing mill 8. In the following description, a constant inner diameter tube with tapered ends will be called a tapered end tube, for brevity.

Positioned between the furnace and the piercing mill 2 is an inclined grate 9 for bringing heated billets from the furnace to the piercing mill 2. Located between the piercing mill 2 and the longitudinal tube rolling mill 3 is an inclined grate 10 for the transfer of hollow billets from the piercing mill 2 to the longitudinal rolling mill 3. A similar grate 11 serves to transfer the tubes from the longitudinal rolling mill 3 to the rolling-off mill 6. Installed on the outlet from the rolling-off mill 6 is a roller conveyor 12 to transfer the tubes from the rolling-off mill 6 to the furnace 7 and the stretch-reducing mill 8.

In the device (FIG. 2) for producing semi-product tapered end tubes, the rolling mill comprises bottom and top rolls 5 and 5 installed in a bed 13 and driven from a constant or variable speed motor (not shown in FIG. 2). The rolls 5 and 5' are provided with grooves of semi-circular form in cross section. The top roll 5 is installed for possible displacement in a vertical plane to alter the clearance between this roll and roll 5, before rolling, by means of pressure screws 14, while in the process of rolling, by means of an individual drive provided for the purpose. This drive provides a gradual displacement of the roll 5 in the direction of altering the clearance between the rolls 5 and 5 in the course of tube end rolling and holding the rolls in the positions corresponding to the minimum and maximum clearance therebetween. The above drive includes two hydraulic cylinders 15 (FIGS. 2 and 3) and a hydraulic system of operate the cylinders. Each hydraulic cylinder 15 consists of a casing 16 and a piston 17.

Positioned on the hydraulic cylinder casing 16 on the side of the piston 17 is a plug 18, entering the casing 16, the plug being provided with a shoulders 19. Placed between the shoulders 19 and the casing 16 is a wedgeshaped gasket 20 capable of displacing along the casing 16 by means of a screw pair (not shown) and locked in the given position with the help of said pair. Displacement of the wedge-shaped gasket 20 alters the position of the plug relatively to the hydraulic cylinder, thus adlO justing the hydraulic cylinder stroke. The top pressure screw 14 holds the plug 18 in the given position.

Installed on journals 21 (FIG. 3) of the top roll 5 are pads 22 which are spring-biased to the hydraulic cylinders. Slidable on the pads 22 is a gasket 23 with two wedge-shaped portions 24 and 25. Installed on the gasket 23 are the hydraulic cylinders 15 whose operation alters the clearance between the rolls 5 and 5'. For idle passing of the tube between the rolls, the latter are parted and the gasket 23 is removed.

Positioned between the rolls 5 and 5 (FIG. 2) is the short arbor 4 held by a rod 26. The mill 3 has a trough 27 receiving the tube, before and after rolling in the rolls. The tube after being rolled, is returned to the trough 27 by means of return feed rollers 28.

The hydraulic system (FIG. 4) serving the hydraulic cylinders 15 comprises a hydraulic fluid reservoir 29, a pump 30, a hydropneumatic accumulator 31, a relief valve 32, a reversing valve 33, throttle valves 34,35,36, and 37, a filter 38 and two-way pilot valves 39 and 40.

The reversing valve 33 incorporates two electromagnets 41 and 42 operated through the drive control system (not shown in FIG. 4) to engage and disengage the reversing valve 33 for the purpose of reversing the hydraulic cylinders 15.

Pilot valves 39 and in cooperation with throttle valves 34, 35, 36 and 37 permit individual speed control of the hydraulic cylinders 15 at the first and second pass of the tube in the mill 3.

Throttle valves 34,35, 36 and 37 installed on the delivery and return hydraulic lines minimize the effect of rigid pipelines connected to the cylinders on the character of the displacement of the hydraulic cylinders and the top roll 5 connected thereto.

The drive operation is monitored through the control system illustrated diagrammatically in FIG. 5. This control system includes a tube end position sensor 43 installed behind the rolls (also see FIGS. 1 and 2). This sensor identifies the position of the tube from end and generates a signal to commence a gradual parting of the rolls 5 and 5' from a minimum to maximum clearance therebetween and also identifies the position of the tube rear end to generate a signal to reduce the clearance between the rolls to the given minimum value. Principally, in rolling single-size tubes, parting of the rolls and bringing the rolls together can be effected only by using signals transmitted by the sensor 43. However, for rolling various-size tubes, the control system is provided with a drive engaging unit 44 having a roll displacement start setter 45 to give commands to deliver fluid to the hydraulic cylinders in the required direction to increase or reduce the clearance between the rolls 5 and 5', and also to preset a delay value for signals of the roll displacement start sensor 43. The unit 44 is connected to the actuating mechanism (in this embodiment to electromagnets 41 and 42) for opening the reversing valve 33 in parting or bringing together the rolls.

ln addition, the control system comprises a tube end tapered section length control unit 46 whose output signals come to a unit 47 of the hydraulic cylinder speed control to vary the displacement speed of the rolls a roll displacement start control unit 48. For more convenient operation of the system, the latter is provided with a unit 49 to indicate actual signal delays, roll displacement start and tapered section length.

To monitor the above units, the control system apart from said tube end position sensor 43 includes roll extreme position sensors 50 and 5] (refer also to FIG. 2), a roll load sensor 52 and a tube pass number sensor 53.

Because the roll extreme position sensors 50 and 51 correspondingly indicate the minimum and maximum clearance, in the further description they will also be called minimum and maximum clearance sensors.

The sensor 43 indicating the positions of the tube ends relatively to the rolls when the tube travels towards the rolls serves to generate a signal to part the rolls when the sensor active zone is entered by the tube front end (as viewed in the rolling direction and also to generate a signal to bring together the rolls when the tube rear end leaves the sensor active zone. In the given version of the automatic control system, the sensor 43 accomodates an element 54 to identify the tube rear end passing moment and an element 55 to identify the tube front end passing moment. These two elements readily solve the problem of interlocking the entire control system in returning the tube by the return feed rollers 28 to the trough 27.

The roll displacement start and end moments are checked by sensors 50 and 51 (refer also to FIG. 2) of the minimum and maximum (at the given displacement) clearance between the rolls. ln rolling thinned end tubes, pressure screws 14 (FIGS. 2 and 3) and components connected thereto are kept stationary. Therefore, the maximum clearance sensor 51 is installed on the pressure screw or components connected thereto.

With the rolls positioned for the minimum clearance therebetween, within the entire displacement range, the distance between the shoulder 19 of the plug 18 and the casing 16 ofthe cylinder 15 is kept unchanged. Owing to this, the sensor 50 of minimum clearance between the rolls 5 and 5 can be installed on the housing 16 of the cylinder 15 to check positions of maximum departure of the shoulder 19 of the plug 18 from the hydraulic cylinder casing.

Sensors 50 and 51 of the maximum and minimum clearance between the rolls may be of any design and principle of operation which arecapable of sensing relative displacement with an error not greater than 0.1

To check the coincidence of moments of roll displacement start with the given tube cross-section, it is important to identify accurately the moments of gripping the tube by the rolls and those of the tube leaving the rolls. A load sensor 52 accomplishes the function. Load cells used for load measuring purposes are suitable for the role of this sensor. Such a sensor may be installed, say, under the pressure screws of the mill (refer to FIG. 2).

Actual lengths of the thinned ends and errors of roll displacement start are controlled through discrete values. For this purpose, the control system incorporates a variable electric pulse generator 56. Each pulse produced by this generator corresponds to a certain length increment (for example one centimeter) of the tube being rolled. The electric pulse frequency of the generator 56 corresponds to the rolling speed expressed in cm/s or in other readily countable units, for which purpose the generator frequency is adapted to vary depending on the rotations-per-time-unit speed of the rolls and the mean slip factor of metal relatively to the rolls.

In the longitudinal rolling mill. tubes are usually rolled on a short arbor in two passes, that is the tube is initially rolled between the rolls 5 and 5 and arbor 4. Then, by means of the gasket 23, the rolls are parted to return the tube idly to the trough 27. Here the tube is turned through By means of the gasket 23, the rolls are brought together. The tube is again delivered to the rolls for second-pass rolling. Stretch is not equal in the first and second passes and therefore the automatic control system should take account of the exact pass the tube is being rolled. Pass number sensor 53 included in the control system accomplishes function. This sensor is installed on the gasket 23 for rolling tubes on a single-size arbor, or on the arbor changing mechanism (not shown) if the first-pass rolling is effected on one size arbor while the second-pass rolling is effected on another size arbor.

A description will be given now of the units incorporated in the automatic control system of the roll displacement drive.

The drive engaging unit 44 (H6. 6) is designed to generate commands to part or bring together the rolls after a given time delay upon the appearance of signals from elements 54 and 55 of the tube end position sensor 43. The unit 44 actuates the electromagnets 41 and 42 of the reversing valve 33 to make the certain spaces of hydraulic cylinders communicating with the highpressure accumulator 31, and other certain spaces with the return line.

The drive engaging unit 44 has two inverters 57 and 58 series-connected on the output of element 54 of the tube end position sensor 43, to identify the rear end of the tube when the latter travels toward the rolls. Connected to the second input of the inverter 58 is element 55 of the sensor 43, to identify passing of the tube front end, while the output of the inverter 58 is connected to the operating input of a flip-flop 59. These inverters are blocking the drive engaging unit when the tube is being returned to the trough by the return feed rollers. Should the element 54 act first and the element 55 second, which corresponds to the tube travelling toward the rolls, a signal produced by the element 54 sets the flip-flop 59. In returning the tube, first a signal appears from the element 55 on the input of the inverter 58 to exclude a signal from the element 54 of the tube end position sensor 43 reaching the flip-flop 59. The output of the flip-flop 59 is connected to a coincidence circuit 60 intended for connecting an electric pulse generator 56 via an OR" element 6] to the electric pulse counter 62 when signals are found on all three inputs of the coincidence circuit 60.

Outputs of the pulse counter 62 are connected to groups 63, 64,65 and 66 of the coincidence circuit, which in turn are connected to the delay setter 45. When the counter 62 receives the same number of pulses which is contained in the delay setter 45 for the tube front end in the first rolling pass, a signal occurs on the output of the group 64 of the coincidence circuit which, via an OR element 67, comes to the operating input of the flip-flop 68. The output of the flip-flop 68 is connected to the electromagnet 41 of the reversing valve 33 to actuate the drive to part the rolls for the time a signal remains on the output of the flip-flop 68. Besides, the output of the flip-flop 68 is connected to the reset input of the flip-flop 59 to disconnect the generator 56 from the counter 62 at the moment the electromagnet 41 is switched on. A signal from the output of the flip-flop 68 via the OR" element 69 cancels information accumulated in the counter 62.

Inputs of the groups 63 and 64 of coincidence circuits are connected to the pass number sensor 53, and the group 64 is directly connected while the group 63 is connected via the inverter 70 to cut in the group 64 in the first pass of the tube and to cut in the group 63 in the second pass.

In addition, inputs of groups 63 and 64 of the coincidence circuits are connected to the output of the flipflop 59 which is actuated only in rolling the tube front end, thus providing the required selectivity of the groups.

A flip-flop 71 is connected to the output of the inverter 58 and serves to memorize a signal from the element 54 at forward tube travel as long as the process of bringing together the rolls continues when rolling the rear thinned end.

A coincidence circuit 72 is connected through its inputs to the output of the flip-flop 71, to the electric pulse generator 56 and to the output of the inverter 57, and serves to connect the generator 56 to the counter 62 after the tube rear end leaves the active zone of the element 54 of the tube end position sensor 43. From this moment on, the counter 62 receives pulses. When the counter accumulates the same number of pulses as preset in the delay setter 45, a signal occurs on the output of the group 65 in the first rolling pass and on the group 66 of the coincidence circuits which, via an OR element 73, sets the flip-flop 74. Selectivity of groups 65 and 66 of the coincidence circuits is obtained due to their connection to the pass number sensor 53 resulting in the group 65 operating with the first tube rolling pass in the mill, and in the group 66 of the coincidence circuits operating with the second tube rolling pass. In addition, the outputs of groups 65 and 66 of the coincidence circuits are connected to the output of the inverter 57, thus permitting operation of these groups only when rolling the rear thinned end of the tube.

The output of the flip-flop 74 is connected to the electromagnet 42 of the reversing valve 33 to actuate the hydraulic system to bring together the rolls and 5 when rolling the rear thinned end. Apart from that, the output of the flip-flop 74 is connected to the reset input of the flip-flop 71 to discontinue sending pulses from the generator 56 to the counter 62. The output of the flip-flop 74 is connected also to the cancel input of the counter 62 via the OR" element 69.

The reset input of the flip-flop 68 is connected to the sensor 51 of the maximum clearance between the rolls. This connection aims at switching off the electromagnet 41 at the termination of parting of the rolls. For the same purpose, the reset input of the flip-flop 74 is connected to the minimum clearance sensor 50.

The delay control unit 48 is diagrammed in FIG. 7. The purpose of the union elements will become more readily understood after perusal into possible errors illustrated in FIG. 8; A case is illustrated in FIG. 8a when parting of the rolls starts later than the moment of gripping the tube by the rolls, while bringing the rolls together terminates earlier than the tube leaves the rolls. A case is illustrated in FIG. 8b when parting of the rolls starts earlier than the gripping moment, while bringing the rolls together terminates later than when the tube leaves the rolls. Cases are also possible when the error sign on one end of the tube is opposite to that on the other end of the tube.

The first stage of error control determines an error sign. A coincidence circuit 75 is connected to the load sensor 52 and to the sensor 50 of the minimum clearance between the rolls and generates a signal in case of the error character shown in FIG. 8a, while a coincidence circuit 76 connected to the same sensors via inverters 77 and 78 generates a signal in case of errors shown in FIG. 8b.

The second stage of error control takes account of tube rolling pass number in the mill, for which purpose the coincidence circuits with one input are connected directly to the tube pass number sensor 53 and become actuated with the first tube pass, while the coincidence circuits 81 and 82 are connected to the sensor 53 via an inverter 83 and become actuated with the second tube pass.

The third stage of error control determines the actual end of the tube where an error occurred during the rolling thereof. In rolling the tube front end, there is always a signal from the element 54 of the tube end position sensor 43, whereas in rolling the tube rear end, there is always no signal from this element.

Inputs of the coincidence circuits 84 to 91 are connected to outputs of the coincidence circuits 79, 80, 81 and 82 and to the element 54 of the tube end position sensor 43. With this, inputs of the coincidence circuits 84, 85,88 and 89-are connected directly to the element 54 and control an error on the tube front end, while inputs of the coincidence circuits 86, 87, 90 and 91 are connected to the element 54 via an inverter 92 and control an error on the tube rear end.

In the case when the rolling technology requires, apart from producing tapered sections, also that of thinned cylindrical sections on tube ends, the delay control unit may have four electrical means 93, 94, 95 and 96 of error determination and for switches 97, 98, 99 and 100. These means are intended for setting the given lengths of the cylindrical sections of the tube ends and automatic correction of the setter tuning to obtain the required delay values.

Switches 97, 98, 99 and 100 in one position connect the outputs of coincidence circuits 101, 102, 103 and 104 to the engaging unit 44 (as shown in FIG. 7) in the case of rolling tubes without cylindrical end sections and in another position these switches connect the outputs of means 93, 94, 95 and 96 via OR circuits 105, 106, 107 and 108 to the engaging unit 44 in the case of rolling tubes with cylindrical end sections.

Coincidence circuits 109 to 112 are connected to the unit 44 via OR38 circuits to 108 and pulses from the generator 56 through them go to the engaging unit in rolling the tapered end.

Delay error determination means 93 to 96 are used for setting the length of the cylindrical portions of tube ends. All these means are identical and therefore only one is diagrammed in FIG. 9.

The error determination means comprises a coincidence circuit 113 connecting the electric pulse generator to a counter 115 for the period of rolling the cylindrical section. A signal equal in time duration to the period of rolling the cylindrical section is brought to the input X,. A correction is turned out in those cases when the number of pulses entering the circuit is over or below the number preset in the counter 115. The counter installed in this circuit has a variable output, that is, it incorporates a switch by means of which the elements following the counter can be connected to any output within the counter capacity.

The variable output of the counter 115 is connected to the input ofa flip-flop 116 intended for sending, via a coincidence circuit 117 to the setter 45, pulses exceeding the number thereof set in the counter 115. A coincidence circuit 118 is connected to the electric pulse generator 56 and flip-flops 116 and 119 and is intended for transmitting pulses to the setter 45 if the number of pulses entering the counter 115 for the period of the signal kept on the input X, is below that preset in the counter 115. To connect the coincidence circuit 118 to the setter 45 and via an "OR circuit 114 to the counter 115 upon termination of the signal on the input X,, the error determination means incorporates a one-shot multivibrator 120 which, upon termination of the signal on the input X sets the flip-flop 119. When the counter 115 receives the given number of pulses, the flip-flop 116 out off the coincidence circuit 118.

Input X is intended for resetting the counter 115 and flip-flop 116. In the example being explained, this input is connected to the sensor 53 of the tube pass number in the mill.

The signal delay setter consists of four similar circuits, one of which is disclosed in FIG. 10. A reversible counter 121 is adapted for varying the set number within the possible range of time delays expressed in pulses. The variable output of the counter is connected to one of the inputs of a flip-flop 122 intended for use in cooperation with pulse shapers 123 and 124 and a button 125 for filling the counter before starting operatlon.

The pulse shaper represents a circuit on whose output a pulse of the given shape occurs when the input is deenergized. After the given number is set in the counter 121, the button 125 is applied to energize the input of the pulse shaper 123 for a short time. Upon switching off the button 125, a pulse occurs on the output of the shaper 123 to operate the counter 12]. Upon termination of this pulse, a pulse appears on the output of the shaper 124 and sets the flip-flop in such a position at which that a signal occurs on its output. The output of the flip-flop 122 is connected to the input of a coincidence circuit 126, and pulses from the electric pulses generator 56 go to the counter 121 until a signal appears on the variable output of the counter. This signal alters the position of the flip-flop 122 to discontinue the flow of pulses to the counter.

Pulses fed to the input of the reversible counter 121 from the delay control unit 48, on the pulse addition input or on the pulse subtraction input, after the earlier preset number in the counter. All outputs of the reversible counter are connected to the groups of coincidence circuits of the engaging unit 44.

The thinned end length control unit 46 (FIG. 11) comprises a flip-flop 127 whose input is connected to the sensor 50 of the minimum clearance between the rolls, while the output is connected to a coincidence circuit 128. Connected to the second input of the coincidence circuit 128 is the sensor 50 via an inverter 129. This wiring of the elements permits a signal to be established on the output of the coincidence circuit 128 from the moment at which the rolls start parting until the rolls reach the position of maximum clearance therebetween. when a signal appears on the output of the sensor 51 of maximum clearance between the rolls. which transfers the flip-flop 127 to the second steady state.

Inputs of coincidence circuits 130 and 131 are connected to the output of the coincidence circuit 128 and also to the pass number sensor 53, whereas the coincidence circuit 131 is connected to this sensor directly the coincidence circuit 130 is connected thereto via an inverter 132.

A signal appears on the output of the coincidence circuit 131, being in duration equal to the period of parting the rolls at the first rolling pass of the tube in the mill, while a signal appearing on the output of the coincidence circuit 130 is equal in duration to the period of parting the rolls at the second rolling pass. Coincidence circuits 130 and 131 are connected respectively to the inputs of the error determination means 133 and 134 and the electric pulse generator 56 connected thereto for the period of parting the rolls.

Basically the means 133 and 134 are circuited as shown in FIG. 9. Correction signals are fed from the outputs of these means to the unit 44 for adjusting the roll parting speed at the first and second tube passes to vary the setting of the throttle valves determining the roll parting speed.

A flip-flop 135 connected by its input to the sensor 51 of maximum clearance between the rolls and by its output to a coincidence circuit 136 serves, in cooperation with an inverter 137, to produce a signal on the output of the coincidence circuit 136 being in duration equal to the period of the rolls being brought together. Coincidence circuits 138 and 139 serve to transmit a signal from the output of the coincidence circuit 136 to one of error determination means 140 and 141 depending on the number of the tube pass in the mill for which purpose the inputs of the coincidence circuits 138 and 139 are connected to the pass number sensor 53.

From the outputs of the error determination means 140 and 141, corrections are transmitted to the roll displacement speed control unit 47 for setting the throttle valves which determine the speed of bringing the rolls together in rolling the given end of the tube at the first and second pass of rolling the tube in the mill.

The rolling-off mill (FIG. 1) is a diagonal type mill in which the tube wall is rolled off between rolls 142 and 142' and an arbor 143 held by a rod 144. For rolling off the wall of the cylindrical portion of the tube and the thinned end sections thereof, at least one of the rolls is provided with a drive to ensure the displacement of the rolls according to the given law in the direction of altering the clearance therebetween in rolling the tube ends. The above mentioned drive has a hydraulic motor 145 connected through a reduction unit 146 to pressure screws 147.

The hydraulic motor effects the drive quick-acting with a wide range of speed control.

The hydraulic system (FIG. 12) powering the hydraulic motor 145 includes a hydraulic fluid reservoir 148, pump 149, hydropneumatic accumulator, relief valve 151, reversing valve 152, throttle valves 153 and 154 and filter 155.

The reversing valve 152 has two electromagnets 156 and 157 which are supplied with electric current from the drive control system serving to engage and disengage the reversing valve for the required direction of rotation of the hydraulic motor 145.

The roll drive hydraulic system of the rolling-off mill is operated through a control system diagrammed in FIG. 13. This control system includes a tube rear end position sensor 158 installed behind the rolls (refer also to FIG. 1) generating a signal to start the rolls 142 and 142 for a gradual bringing together from the maximum clearance between the rolls to the minimum given one and a load sensor 159 generating a signal within the time period of rolling the tube in the rolls and also generating a signal for parting the rolls from the initial clearance to the maximum given clearance between the rolls 142 and 142' in rolling the front end of the tube.

The control system of the roll displacement hydraulic drive in the rolling-off mill for rolling-off thinned ends of tubes (FIG. 13) includes a roll engaging unit 160 connected to the actuating mechanism (electromagnets 156 and 157 in the given example) to open the reversing valve 152 in parting and bringing together the rolls.

In addition, the control system incorporates a unit 161 to control the length of the tube end thinned sections whose output signals are transmitted to a unit 162 for the rotation speed control of the hydraulic motor 145 to vary the displacement speed of the rolls 142 and 142' and a unit 163 for the roll displacement start delay control. For more convenient attendance of the system, there is provided a unit 164 to indicate the actual roll displacement start signal delays and the lengths of tapered ends. The delay values are set in a delay setter 165 connected to the delay control unit 163 and the engaging unit 160.

To monitor the above units, the control system, in addition to the sensors mentioned, includes a sensor 166 of the rotation speed of the hydraulic motor 145 to permit control over the displacement of the rolling-off mill rolls. This sensor may be represented by any contactless sensor whose sensitivity zone is entered by a part connected to the motor shaft.

Control over the actual lengths of thinned ends and roll displacement start errors is effected in discrete values. For this purpose, the roll displacement drive control system in the rolling-off mill is provided with a variable electric pulse generator 167. Each pulse produced by this generator corresponds to a certain length increment (for example, 1 centimeter) of the tube being rolled. The frequency of the electric pulse generator 167 corresponds to the rolling speed expressed, say, in cm/s or in other units convenient for counting and for which purpose the generator frequency is varied depending on the roll rotation speed, mean slipping factor of metal in relation to the rolls and roll incline angle.

The engaging unit 160 serves to produce commands for parting and bringing together the rolls of the rollingoff mill on receiving signals from the load sensor 159 and the tube rear end sensor 158.

The engaging unit 160 (FIG. 14) includes a coincidence circuit 168 whose input is connected to the load sensor 159, tube rear end position sensor 158 and electric pulse generator 167. This circuitserves to connect the electric pulse generator 167 to a counter 169 of these pulses at the moment the tube is gripped by the rolls. Connected to the counter output is a group 170 of coincidence circuits which produces a signal for cutting in a flip-flop 171 when simultaneously two signals appear on one of the coincidence circuits of the group 170, one from the setter 165, the other from the counter 169. A signal sent by the flip-flop 171 actuates the electromagnet 156 of the reversing valve 152 for parting the rolls and keeps it energized until a signal arrives from the flip-flop 172 to indicate that the given displacement of the rolls has been accomplished.

Control overall the rotation speed of the hydraulic motor 145 proportional to the displacement of the rolls is effected by a reversible counter 173 whose inputs are connected via coincidence circuits 174 and 175 to the rotation speed sensor 166, and while the circuit 175 connects the sensor 166 to the addition input of the reversible counter 173 at parting the rolls over the front thinned end of the tube, the coincidence circuit 174 connects the sensor 166 to thesubtraction input of the reversible counter 173 in bringing together the rolls over the rear end of the tubes.

The reversible counter 173 is adapted for the preliminary setting of the number of revolutions of the hydraulic motor 145 to correspond to the given displacement of the rolls during their parting and bringing together. After the reversible counter 173 has received the given number of pulses from the hydraulic motor rotational speed sensor 166, a signal appears on one of the outputs of the counter changing the state of the flip-flop 172. One of the outputs of the flip-flop 172 is connected to the reset input of the flip-flop 171. This link is used to give a command to stop the hydraulic motor upon completion of the given displacement of the rolls.

A coincidence circuit 176 connected to the tube rear end sensor 158 via an inverter 177 serves to connect the electric pulse generator to a counter 178 of these pulses when the tube rear end leaves the active zone of the tube rear end sensor 158. The output of the counter 178 is connected to a group 179 of coincidence circuits which serves to actuate a flip-flop 180 after the counter has received the same number of pulses which is set in the setter 165. The reset input of the flip-flop 180 is connected to one of the outputs of the flip-flop 172. This link is used to transmit a command to stop the hydraulic motor after it has made a certain number of revolutions preset in the reversible counter 173.

The outputs of flip-flops 180 and 171 are connected to the tube thinned end length control unit 161. These links are used to transmit signals from the unit 160 to the thinned end length control unit 161, which in their time duration are equal to the operation period of the electromagnets 156 and 157 during the parting and bringing together of the rolls.

The outputs of flip-flops 171 and 172 are connected to the delay control unit 163. These links are used to transmit signals from the engaging unit 160 to the delay control unit 163, indicating that the rolls 142 and 142' are in the minimum clearance position.

The delay control unit 163 (FIG. 15) includes a flipflop 181 whose inputs are connected to the unit 160 and which serves to generate a signal on one of the outputs if the rolls 142 and 142 are in the position of minimum clearance therebetween and a signal on the second output if the rolls are in the maximum clearance position. Coincidence circuits 182 and 183 are connected to the load sensor 159 and while the coincidence circuit 182 is directly connected, the coincidence circuit 183 is connected via an inverter 184. These elements of the unit 163 serve to determine the sign of error. If the rolls are in the position of minimum clerance therebetween and the tube is already between the rolls which is sensed by the load sensor 159, a signal appears on the output of the coincidence circuit (plus sign error).

If the rolls 142 and 142' are not in the position of minimum clearance therebetween and there is no signal from the load sensor 159, a signal appears on the output of the coincidence circuit 183 (minus sign error).

There cannot be any minus sign error with the front end of the tube because parting the rolls is commanded by a signal from the load sensor 159. Therefore, the error duration with the front end of the tube is determined by only a coincidence circuit 185 while the rear end of the tube the error duration is determined by two coincidence circuits 186 and 187. The coincidence circuit 185 is directly connected to the tube rear end sensor 158, while the coincidence circuits 186 and 187 are connected to this sensor via an inverter 188. The delay control unit 163 has two error determination means 189 and 190 diagrammed in FIG. 9 and intended for setting delays in the start of displacing the rolls of the rolling-off mill in those cases in which tubes with cylindrical sections on thinned ends are being rolled. The input of means 189 and 190 receives signals from the output of the coincidence circuits 185 and 186, whose duration is equal to a time error. In rolling tubes with cylindrical sections on thinned ends, corrections to the preliminary setting of the setter 165 are transmitted from the means 189 and 190 via switches 191 and 192 to the setter 165.

When operating with no cylindrical sections on tube ends, coincidence circuits 193, 194 and 195 connect the electric pulse generator 167 to the roll displacement start delay setter 165 for a period equal to the duration of the tube error rolling. The outputs of the coincidence circuit 195 and the means 190 are connected to the unit 165 via an OR circuit 196.

The delay setter 165 is basically composed the same as shown in FIG. 10 but comprises only two identical circuits.

The tube thinned end length control unit 161 (FIG. 16) consists of two error determination means 197 and 198 whose design is diagrammed in FIG. 9. The means 197 serves to produce corrections for the roll displacement speed control unit 162 in rolling the front thinned end of the tube, while the means 198 does this in rolling the rear thinned end.

Tube rolling on an installation incorporating the device pursuant to the present invention is carried out as follows.

Billets heated to the required temperature are delivered from the furnace 1 along the inclined grate to the piercing mill wherein the billets are pierced to form hollow billets. The billet piercing process does not differ from the known procedure.

Along the inclined grate 10, the hollow billet is brought to the trough 27 of the longitudinal rolling mill 3. The tube rolling process carried out on this mill substantially differs from the known procedure. Before rolling, the rolls 5 and 5 are installed in such a position by means of the pressure screws 14 at which the given squeezing of the walls is obtained for rolling the tube in the mill. Then, by displacing the wedge-shaped gasket 20, the stroke of the hydraulic cylinders 15 is adjusted to be equal to the double value of the given thinning of the wall of the tube ends. The electromagnet 42 of the reversing valve 33 is actuated for a short-time with a result that the rodless spaces of the hydraulic cylinders 15 are made communicating with the hydropneumatic accumulator 31 while the rod spaces of the hydraulic cylinders are opened to the return line. The hydraulic cylinders 15 together with the roll 5 are displaced and a clearance is established between the rolls equal to the minimum value.

Switches 97, 98, 99 and in the roll displacement start delay control unit 48 are set with respect to the shape of thinning required on the ends of the tube. The values of roll displacement start delays in parting and bringing together are set in the delay setter 45 and the given lengths of the front and rear thinned ends are set in the thinned end length control unit 46 and a preliminary adjustment in performed by throttle valves 34, 35, 36 and 37 determining the speed of parting and bringing together the rolls with the first and second pass of the tube in the mill. This being done, the preparation of the longitudinal tube rolling mill 3 is finished.

With the tube delivered in the rolls, the first to act is the element 54 of the tube end position sensor 43 whose signals are setting the flip-flops 59 and 71 of the engaging unit 44. As the tube travels toward the rolls, its front end enters the active zone of the element 55 of the sensor 43 which is a signal for parting the rolls. The signal of this sensor actuates the coincidence circuit 60 to connect the electric pulse generator 56 to the counter 62. When signals appear simultaneously on all inputs in one of the coincidence circuits of the group 64 of coincidence circuits together with a signal from the setter 45 on one of the inputs, a signal occurs for a short time of the output of the group to set the flipflop 68 and actuate the electromagnet 41 of the reversing valve 33. The hydraulic cylinders 15 and the roll 5 together with them start displacing in the direction of increasing the clearance between the rolls 5 and 5.

'When the roll 5 reached the position of maximum clearance between the rolls, a signal from the sensor 51 of the maximum clearance between the rolls resets the flip-flop 68 and cuts off the electromagnet 41. With this position of the rolls, the middle cylindrical portion of the tube is being rolled. As the tube travels on its rear end leaves the active zone of the element 54 of the tube end position sensor of the inverter 57, the coincidence circuit 72 is cut in to connect the electric pulse generator 56 to the counter 62.

There is a signal from the delay setter 45 on the input of one of the circuits in the group 65 of the coincidence circuits. When another input of the same coincidence circuit has a signal from the counter 62, the flip-flop 74 is actuated as well as the electromagnet 42 of the reversing valve 33. The reversing valve takes such a position at which the rodless spaces of the hydraulic cylinder communicate with the hydropneumatic accumulator 31, while the rod spaces of the hydraulic cylinders communicate with the return line. The roll 5 starts displacing in the direction of increasing the clearance between the rolls.

Thus, the rear thinned end of the tube is being rolled. After the tube is rolled, the gasket 23 with the wedgeshaped portions 24 and 25 is displaced, the roll 5 is raised and rollers 28 return the tube to the trough 27.

During the return, the first to appear is a signal from the element 55 of the tube end position sensor 43, and then appears a signal from the element 54 of the same sensor. This succession of signals prevents operation of the control system because a signal from the element 55 found on the input of the inverter 59 blocks off the signal from the element 54.

In the trough 27, the tube is turned through 90. By displacing the gasket 23, the roll is brought to the operating position, the two-way slide-valves 39 and 40 are actuated to engage the second pair of throttle valves determining the displacing speed of the roll at the second pass of the tube in the mill and the tube is again brought to the rolls. Operation of the control system of the roll displacement drive at the second pass is similar to the procedure described above for the first pass. However, groups 63 and 66 of the coincidence circuits are cut in at the second pass to permit setting other delays of signals from elements 54 and 55 of the sensor 43 by means of the setter 45.

During the first and second pass tube rolling, the preliminary set delays of signals from the sensor 43 for parting and bringing together the rolls are being checked with automatic corrections of these delays and for which purpose, the control system includes the delay control unit 48 whose function has been described together with its basic design.

In addition, during the tube rolling process, the lengths of the tube thinned ends are being checked with the automatic correction of the position of the throttle valves determining the displacement speed of the rolls in their parting and bringing together and for which purpose, the control system includes the thinned end length control unit 46 and the roll displacement speed control unit 47.

Upon completion of the second pass rolling of the tube in the rolls of the longitudinal rolling mill 3, the tube with the thinned wall on its ends is returned to the trough 27 and further along the inclined grate 11 is transferred to the rolling-off mill 6.

Rolling-off tubes with thinned ends differs from rolling regular tubes. Rolls 142 and 142' of the rolling-off mill 6, after the adjustment of the mill similar to that of the known mills, are displaced in the direction of reducing the clearance between the rolls through the same value as in the longitudinal rolling mill 3 with the given size of the tube. The reversible counter 173 is set for a certain hydraulic motor rotational speed to correspond to the given displacement of the rolls, the delay setter 165 is set for approximate values of the delays of the signals from the sensors 158 and 159 and the throt tle valves 153 and 154 are approximately set to control the speed of parting and bringing together the rolls and also the error determination means 197 and 198 are set for the given lengths of the thinned sections of tube ends.

With the tube entering the rolls, the rear tube end sensor 158 acts and its signal prepares for operation the coincidence circuits 168 and 175 used in rolling the front thinned end of the tube. At the moment the tube is gripped by the rolls, a signal appears on the output of the load sensor 159 by which the coincidence circuit 168 connects the electric pulse generator to the counter 169 of these pulses, while the coincidence circuit 175 connects the hydraulic motor rotational speed sensor 166 to the reversible counter 173.

After the counter 169 receives the same number of pulses which has been set in the setter 165, a signal appears on the output of the group 170 of the coincidence circuits which actuates the flip-flop 171 and the electromagnet 157 of the reversing valve 152. With this position of the reversing valve, the hydraulic motor rotates in the direction at which the rolls of the rolling-off mill are displaced in the direction of increasing the clearance between the rolls. When the hydraulic motor has accomplished a certain number of revolutions set in the reversing counter 173, an output signal from the counter sets the flip-flop 171. The electromagnet is cut off and the hydraulic motor stops.

The middle cylindrical portion of the tube is rolled with the rolls parted.

After the rear end of the tube leaves the active zone of the tube rear end sensor 158, a signal from the inverter 177 cuts in the coincidence circuits 174 and 176. The coincidence circuit 176 connects the electric pulse generator 167 to the counter 178 and the coincidence circuit 174 connects the hydraulic motor revolution counter to the reversible counter 173. With the counter 178 receiving the same number of pulses as set in the setter the flip-flop 156 of the reversing valve 152 is cut in and the rolls of the mill are brought together. The electromagnet 156 is cut off after the hydraulic motor 145 has accomplished the numberof revolutions preset in the reversible counter 173.

During the tube rolling-off process, the actual lengths of thinned sections on tube ends is being checked and for which purpose, the control system includes the thinned and length control unit 161 with the automatic adjustment of throttle valves 153 and 154' varying the displacement speed of the rolls. in addition, the control system includes the delay control unit 163 with the automatic adjustment of the signal delay setter 165 of the sensors 158 and 159. Operation of units 163 and 161 may be understood from the description of the design of these units.

The indication unit 49 in the control system of the roll displacement drive of the longitudinal rolling mill and the indication unit 164 of the rolling-off mill drive control system are so positioned on the mill that the rolling-off mill control system can be adjusted according to the results of checking the longitudinal rolling mill control system.

After being treated in the rolling-off mill, the tubes with thinned wall on their ends go to the reheating furnace 7 along the transfer roller conveyor 12 and thereafter to the stretch-reducing mill 8 in which the wall is obtained within the allowable thickness limits over the entire length of the tube.

The present disclosure concerns the device for producing semiproduct tubes with tapered thinned end portions. However, for those skilled in the art, it is obvious that by varying the roll displacement speed, it is possible to obtain the tube thinned end of any desirable shape.

What we claim is:

1. An apparatus for forming tubes intermediate of their finished form at a constant inner diameter with end portions of reduced thickness comprising: a twohigh mill having opposing rolls provided with grooves of semicircular form in cross section, plug means located between said rolls, roll adjustment means for altering the gap between said rolls and said plug means, control means for controlling the speed and 

1. An apparatus for forming tubes intermediate of their finished form at a constant inner diameter with end portions of reduced thickness comprising: a two-high mill having opposing rolls provided with grooves of semicircular form in cross section, plug means located between said rolls, roll adjustment means for altering the gap between said rolls and said plug means, control means for controlling the speed and direction of the displacement of said roll adjustment means to taper the end portions of a tube and limiting means for determining maximum and minimum roll gap.
 2. The apparatus as claimed in claim 1 in which the roll adjustment means includes two synchronously operating hydraulic cylinder-piston units with an adjustable stroke, one of said rolls having journals, said cylinder-piston units being operably connected to said journals and displacing said one roll to a position corresponding to the maximum gap and a second position corresponding to the minimum gap and a hydraulic system for operating said cylinder-piston units including controllable throttle valves for adjusting the rate of fluid delivery into the cylinder spaces of the cylinder-piston units.
 3. The apparatus as claimed in claim 2 in which said plug means includes a shoulder and a wedge-shaped gasket mounted for possible displacement between the shoulder and the cylinder and locking in a given position to adjust the stroke of the cylinder-piston unit.
 4. The apparatus as claimed in claim 2 including a thinned end length control unit operably connected to the roll adjustment means and generating signals to vary its speed to alter the roll displacement speed, and a tube end portion position sensor located before the rolls on the side of introducing the tube thereto for sensing the position of the tube front end portion and generating a signal for starting a gradual parting of the rolls from the minimum to the maximum gap and for sensing the position of the tube rear end portion and generating a signal for reducing the gap between the rolls to the minimum gap.
 5. The apparatus as claimed in claim 4 including two roll extreme sensors, a variable electric pulse generator having a frequency proportional to the rolling speed, said length control unit including a counter of electric pulses of said generator, connected thereto via a commutator controlled by said position sensors and by whose signals the commutator connects the counter to and disconnects the counter from the generator whereby the total number of pulses entering the counter is proportional to the end portion length.
 6. The apparatus as claimed in claim 5 in which a pulse number counter having a variable output serves for generating an electric signal when the number of pulses received by the counter deviates from a certain given value.
 7. The apparatus as claimed in claim 6 in which means serves to determine the value and sign of an error in the length of a tube end portion relative to the given value, said means including two parallel electric circuits with coincidence circuits connected to the pulse generator via two flip-flops on the input of each coincidence circuit, one flip-flop being connected to the output of a pulse counter and both coincidence circuits, the other flip-flop being connected to the counter output through the first flip-flop and one of the coincidence circuits so that depending on the state of the flip-flop, one of the coincidence circuits opens while the other remains closed thus resulting in an electric signal appearing on the output of the coincidence circuits to characterize the value and sign of an error.
 8. The apparatus as claimed in claim 1 including tube end portion position sensors, said sensors being defined by two elements sensing the passage of tube end portions, said elements being mounted one after the other in succession on the side of introduction of the tube to the rolls and a drive engaging unit operably connected to said elements operative upon receiving a signal from one of the sensors to generate a signal to part the rolls and upon receivinG a signal from the other sensor to generate a signal to bring the rolls together and the drive engaging unit being provided with means for a time delay of the signal to control the drive engaging moment with respect to the moment of gripping the tube by the rolls and the moment the tube leaves the rolls.
 9. The apparatus as claimed in claim 1 including a first sensor of minimum gap between the rolls and a second sensor of load on the rolls, a control system having a roll displacement start delay control unit connected via its input to said first and second sensors and generating a signal proportional to the time interval between signals of the sensors, the output of the delay unit being connected to a delay means of a drive engaging unit via a delay setter for controlling the delay value with respect to the error in the start of roll displacement.
 10. The apparatus as claimed in claim 5 in which the thinned end length control unit is provided with a plurality of identical delay error determination means, each for effecting control for the front end portion or rear end portion in the corresponding pass of the tube in the mill, the commutator being multi-channel for actuating the corresponding pairs of delay error determination means, and a tube pass number sensor operably connected to the commutator for the switching thereof.
 11. The apparatus as claimed in claim 10 in which the hydraulic system is provided with two parallel connected controllable throttle valves in each line communicating with both spaces of the cylinder, pilot valves for actuating the throttle valves, and the pilot valves being operably coupled to the tube pass number sensor for controlling the succession of their actuation.
 12. The apparatus as claimed in claim 1 including a rolling-off mill adjacent the outlet of the two-high mill, said rolling-off mill having opposed rolls, at least one of the rolls having an adjustable drive for a gradual displacement of the roll, in rolling the tube end portions, in the direction of altering the gap between the rolls for increasing the gap in rolling the front end portion and reducing the gap in rolling the rear end portion and fixing the rolls at maximum and minimum gaps and a roll drive control means operative at such a speed and direction of roll displacement that the shape of tube produced in the two-high mill is followed. 